Color correction in printing multilayer film



Patented Aug. 19, 1941 COLOR CORRECTION IN PRINTING MULTI- LAYER FILM Ralph M. Evans, Rochester, N. Y., assignor to Eastnan Kodak Company, Rochester, N. Y., a corporationyof New Jersey Application August 16, 1940, Serial No. 352302 4 Claims.

This invention relates to printing multi-layer color film and particularly to a method for obtaining` color correction in printing such film.

subtractive method of color photography, the

color separation images are printed in colors complementary'to the colors of the taking filters or the sensitivity of the emulsion layers. In three-color photography the primary colors are considered to be red, green and blue and the color separation images obtainecl from these are printed respectively in blue-green, magenta and yellow colors. If theoretically accurate dyes could be obtained, these dyes should absorb only their complementary colors. The blue-green should absorb the red region of the spectrum and transmit the blue and the green regions. Similarly, the magenta dye should absorb the green region of the spectrum and transmit the blue and the red regions, and the yellow dye should absorb the blue region and transmit the red and the green regions.

Dyes have not yet been found for use in color photography which absorb only in the proper spectral regions. The blue-green dye usually absorbs not only in the red region but also to some extent in the green and the blue regions. The magenta dye absorbs not only in the green region but also in the blue and red regions. The yellow dye, on the other hand, is usually quite eflicient, absorbing very little except in the blue and violet region.

As a result of the light absorption of the bluegreen dye in the blue and green regions of the spectrum, certain corrections must be applied in printing, or a lower concentration of magenta or yellow dye must be used in the print in order to maintain a balance of color in the scale of grays. By using less magenta or yellow dye in the` print than would otherwise be used, the gray scale balance is maintained by the bluegreens-` Greens and blues of the print are deraded with gray and, therefore, are less luminous than they should be, while magentas, yellows and reds are lacking in saturation, that is, are diluted by white.

In the preparation of color separation negatives" or positives by printing from a colored original, such as a multi-color transparency, this degradation of colors may be overcome by the use of masks, that is, thin positives in the case oi' color separation negatives, which are registered with the color separation negative in making the print.` When printing from a. multicolor image on photographic film onto a similar multi-layer film, it is, of course, impossible to use separate masks for the different color separation records since they must be printed simultaneously onto the printing material. If a single mask is used, the registration difiiculties are considerable and in the case of small sized film, such as motion picture film, render this method of color correction impracticable.

I have' discovered a method of color correction which is suitable for printing a multi-color image on multi-layer film onto a similar material and` also in printing onto separate emulsion layers for making color separation records. It is of special utility in duplicating natural color transparencies or natural color motion picture film.

According to this method an emulsion layer s coated integrally with the multi-layer film prior to exposure and is so treated that a negative image can be printed in it after processing the film to a colored image.

In the accompanying drawing a series of sectional views shows the steps in the method of preparing a printing element according to my invention.

The usual type of multi-layer film consists of a support having coated thereon three emulsion layers effectively sensitive respectively to the red, green and blue regions of the spectrum. My invention consists in coating as a top or outer layer on a film of this type a thin emulsion layer which has been fogged prior to coating or which is fogged in a suitablelmanner after coating so that it will be developed in a silver halide developer when the film is developed. In thislayer a low contrast negative is made after the film has been processed to colored images and this negative silver image serves as a mask in printing the colored image. In a suitable manner hereinafter described the masking layer is made color-sensitive, usually red-sensitive, since it is ordinarily desired to correct the deficiency in the spectral transmission in this region of the bluegreen and magenta dyes used in reproduction. This layer may be sensitized to other regions of the spectrum if correction in other ways is desirable. The layer may be sensitized so that it nay be partly exposed to light of one color and partly to light of another color. `According to the `desired form of the process however, the masking layer is made sensitive to red light after color processing of` the film and the film is then exposed through the support with red light so that those portions of the color picture which transmit red light are recorded on the masking layer as darker than those portions which absorb red light. Thus; in addition to recording the natural red light transmission of the yellow and magenta dyes, the red light transmission of the blue-green dye is also recordedon the masking layer. I

Although my process may be used in any color method in which a multi-layer element ls processed so that no image is formed in the masking layer prior to the development of the masking image, my process has been designed for use with a method such as that described in Mannes, Godowsky and Wilder U. S. patent application Serial No. 185.700, filed January 19, 1938. cording to the method described in that application, a multi-layer photographic element cons sting of three emulsion layers sensitized respectively to the red. green and blue regions of the spectrum are coated on one side of a single support. After exposure and negative development of this film, the emulsion layers are selectively fogged and colored images are formed therein. Alter negative development, the bottom redsensitive emulsion layer is exposed through the support to red light and the film is then developed in a blue-green color forming developer which produces a blue-green positive image in the bottom layer. Similarly, the top layer is exposed from the outer side and is developed in a silver image in the first or negative developer and remains in this form during color processing of the film. In the normal processing of a photographic element of this type after colored images are formed in the emulsion layers and silver negative and positive images still remain, these silver images are removed by converting them to a soluble silver salt which is then removed in hypo. This step is modified according to my invention by convertingthe silver in the masking layerto silver halide and then sensitizing the silver halide in this layer to red light by bathing in a suitable sensitizing bath. Before this red sensitization of the masking layer, the silver images in the lower three layers are removed in a bath which does not affect silver halide. Because of the removal of silver from the layers containing the colored images, these layers are no longer sensitive. A printing exposure may, thcrefore, be given through the support, that is, through the colored images, onto thered sensitive masking layer using red light for the exposure. This red light exposure impresses an image of the red transmission of the image dyes on the masking layer and the film is then developed in an ordinary silver halide developer to produce a silver image in the masking layer. The silver halide in the masking layer can then be removed in hypo, leaving pure dye .images in the emulsion layers and a silver masking image in the top layer. This film may then be used for printing onto a multi-layer element or for the preparation of color separation images.

A specific method of carrying out my process will now be described.

A sensitive element such as that shown in the first stage of the drawing is used consisting of a support o of transparent material such as glass, cellulose nitrate, cellulose acetate or other organic acid ester or suitable synthetic resin coated with silver halide emulsion layers l I, I2 and !3 sensitive respectively to the red, green and blue regions of the spectrum. A yellow filter layer (not shown) is incorporated between layers |2 and l'3 to prevent the exposure of layers ll and |2 to blue light in the usual manner. A layer M consisting of an ordinary blue-sensitive gelatino-silver halide emulsion is coated 'over the layer !3. The emulsion comprising the layer M is fogged either by light or chemically, preferably prior to coating.

After exposure in a camera or in a printer in the usual way, the film is developed in an ordinary black and white developer. If the film has been properly exposed, development for ten minutcs at 20 C. in a developer of the following composition is satisfactory:

Grams Monomethyl-p-aminophenolsulfate 6 Hydroquinone 10 Sodium sulfite 50 Sodium carbonate 30 Potassium bromide 5 Potassium thiocyanate 0.5 Water to 1000 cc.

This development produces negative silver images I 5, !6 and ll in emulsion layers ll, l2 and l3 and a uniform silver deposit a in layer M, as shown in the second stage of the drawing. The film is then developed as described in application Serial No. 185,'700 to form colored images in the emulsion layers but the silver is not bleached or removed in the manner described in that application. 'The film then contains a bluegreen and silver image IS in layer ll, a magenta and silver image 20in layer !2, and a yellow and silver image 21' in layer |3 as shown in the third stage of the drawing. The layer !8 is not affected by this treatment and remains in the form in g which it existed as shown in the second stage of the drawing.

The next step is the Conversion of the silver in the masking layer only, to silver halide. This is accomplished by treating for 2 minutes in a solution which may have the following composition:

Quinone grams -2 Potassium bromide do 10 `Sulfuric acid cc 2 Ethyl alcohol cc 10 Ethylene glycol cc 850 Water to 1 liter.

the following:

Potassium bichromate grams 4 Sulfuric acid cc 4 Tlis bleach is permitted to act for about 6 minu es.

The silver halide in the top layer H is then sensitized to red light by bathing for 2 minutes in a solution of the following composition:

Pinacyanol grams 0.008 Pyrldine cc 1 Methyl alcohol cc 75 Benzotriazole grams 1 Water to 1 liter.

The film then exists in the form shown in the fourth stage of the drawing, in which there is a blue-green dye image 22 in layer I |,`a magenta dye image 23 in layer |2, and a yellow dye image 24 in layer l3. Layer M contains a red-sensitive uniform silver deposit 25.

The film is next exposed through the support for about 2 to 3 minutes with red light, such as that transmitted by a Wratten No. 23 or 25 filter. This exposure impresses the red transmission of all of the image forming dyes on the red sensitive silver halide in the top layer !4.

The film is then developed in a black and white developer such as that used in the negative development of the film. This produces a silver masking image 26' as shown in the fifth stage of the drawing. The film is then fixed for about four minutes in hypo, washed for several minutes and dried in warm air. The film then appears as shown in the fifth stage of the drawing with pure dye images 22, 23 and '24 colored respectively blue-green, magenta and yellow in the layers H', I 2 and |3 and silver image 26 in the layer ll. The film is then ready for use in printing onto` suitable color sensitive material.

In printing, the masking layer has the effect of increasing the density of the original locally by an amount in approximate inverse .proportion to the density of the original to red light. Hence the densities of the whites, magentas,` yellows,

rds and other colors having a low density to red 4 light are increased most. The density of the blue-greens, blues and greens which have a high density to red light are increased least. Consequently the highlight density of the original is increased and the density range and gamma are reduced. There is, however, no alteration in hue of any portion since the negative mask is neutral gray silver. Only the densities of various portions are increased, and, since the densities of the blues and greens are increased least, these colors appear relative more luminous.

In addition to the use of silver in the mask, it might be made of dye by any suitable method such as by a color forming development. If it is desiredto use the original for viewing subsequent to printing, the mask may be removed without damage to the original image. If the mask is of silver, a simple bleaching in ferricyanide and hypo is required and if it is composed o! dye it may be removed by a diiferential depth bleach such as those described in Mannes and Gdowsky U. S. Patent 2,059,887.

In addition to the specific method described, modications may be made in my process within the -scope of the appended claims.

I claim:

1. The method of preparing a multi-'color printing element afiording corrected color prints, which comprises exposing to an object to be photographed an element having a plurality of superposed emulsion layers sensitive to different spectral regions and an outer, fogged silver halide layer, developing silver images in all said layers including a uniform silver deposit in said outer layer, forming dyeand silver images in said differently-senstive layers, converting the silver in said outer layer only, to silver halide, removing the silver from said diiTerently-sensitive layers, sensitizing the silver halide in said outer layer to a spectral region other than the blue, exposing said outer layer to light of that color through the dye images in the remaining layers, developing a silver image in said outer layer, and removing the silver halide from the outer layer.

2'. The method of preparing a multi-color printing element affording corrected color prints, which comprises exposing to an object to be photographed an element having three superposed emulsion layers sensitive to different spectral regions and an outer,` fogged silver halide layer, developing silver images in all said layers including a uniform silver deposit in said outer layer, forming positive dye and silver images in said differently sensitive layers by successive color-forming development steps converting the silver in said outer layer only, to silver halide, removing the silver from said diiferently-sensitive layers, sensitizing the silver halide in said outer layer to red light, exposing said outer layer to red light through the dye images in the remaining layers, developing a silver image in said outer layer, and removing the silver halide from the outer layer.

3. In a method of forming a masked multicolor film having an integral, outer, masking layer, the steps which comprise sensitizing the masking layer to a spectral region other than blue after the formation of colored images in emulsion layers of the film, and printing the mask with light of the color to which the masking layer has been sensitized through said colored images.

4. In a method of forming a masked multi-color film having an integral, outer, masking layer,

the step which comprise sensitizing the masking layer to red light after the formation of colored images in emul-sion layers of the film, and printing the mask with red light through said colored images.

RALPH M. EVANS. 

